The World's 20 Most Impressive Fortresses

A fortress protects and gives military personnel a safe harbor from the enemy. But not all fortresses were created equal. And they certainly weren't all created the same. We look over time and distance to find the 20 most impressive fortresses from around the world and throughout history.

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Gibraltar

The legendary geography at the Rock of Gibraltar includes its sheer cliff face, difficult western slope, and location at the southern tip of Europe adjacent to the Strait of Gibraltar. Britain took advantage of this by enhancing medieval structures here, arming and fortifying the top of the rock in the 16th century. Centuries of improvements, including carving tunnels into the rock for armaments, troop movement, and storage, helped Britain to withstand siege attempts. Today the land is still technically a British overseas territory.

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Cheyenne Mountain Complex

Home of NORAD, which monitors pretty much everything in North American airspace, the Cheyenne Mountain Complex uses the mountains around Colorado Springs as fortification. Sitting inside a hollowed-out space in the mountains, the air defense system reached the height of its mystique during the Cold War when it opened in 1967. Its 25-ton blast doors are embedded within the 1,700 feet of granite. After a complete remodel, the buried site reopened for business in 2008.

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Chittorgarh Fort

The largest fort in India covered 700 acres atop a 590-foot-tall hill, complete with towers and walls that have stood since the Maurya Empire built it near the Indian city of Udaipur in the 7th century. Fort Chittorgarh, also dubbed the Fort of Chittor, has a one-mile-long twisty road leading to it with seven gateways guarded by a watch tower and iron-spiked doors. While only 22 of the original 84 bodies of water within the fort still exist, 40 percent of the fort's space was covered by water at one time—enough of a reservoir to hold about one billion gallons of water and, with rainfall, enough to maintain an army of 50,000 for four years without fear of thirst.

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Windsor Castle

The oldest and largest still-inhabited castle in the world, Windsor Castle has been home to British royalty for almost 1,000 years. Now the official residence of Queen Elizabeth II, the castle was built by William the Conqueror in 1070 as a strategic stronghold along the River Thames, guarding the western approach to London high above the river. The stone fortifications were added along the way, allowing the castle, which became a military headquarters building, to withstand multiple battles. Windsor remains a working royal palace, made popular as a royal hunting ground that's close to the capital.

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Fort Jefferson

One of America's largest masonry-built buildings was designed in the mid-1800s to ward off pirates from the Gulf of Mexico shipping lanes. Located on Garden Key way out in the Florida Keys, past Key West, Fort Jefferson is made of more than 16 million bricks. It was a massive upgrade from the lighthouse that originally stood on this spot. The fort was in active use through the Civil War, mainly to house prisoners, but its thick walls weren't as impressive by the late 1800s and it was abandoned as a fort. The structure was never fully finished, but the six-sided fort covers 11 of the 16 acres of land on the key and remains a tourist destination.

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Prague Castle

Built around 880 by Prince Borivoj of the Premyslid Dynasty, Prague Castle stands as the "largest coherent castle complex in the world" at more than 753,000 square feet. Among its structures you'll find palaces and buildings from the Romanesque-style of the 10th century and Gothic architecture from the 14th century. Inside the castle, the St. Vitus Cathedral and St. George's Basilica give this massive fortress extra cultural appeal. Prague Castle has earned its status as an iconic fortress, as wars in the 1600s inflicted major damage upon the structure.

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B-17 Flying Fortress

We just couldn't ignore something with "flying fortress" as the nickname, could we? The Boeing-created four-engine heavy bomber debuted with the U.S. Army Air Corp in 1935 as a new plane loaded with machine-gun mounts and bombing capabilities. The B-17 was designed as a low-wing monoplane with aerodynamic features derived from the XB-15, and the amount of guns, bombs, and heft it carried increased with each model. Stories exist from World War II of pilots flying the plane home with up to 600 flak holes.

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Malbork Castle

The Teutonic Order, a Catholic religious group founded as a military order, constructed the world's largest brick castle in Poland on the bank of the river Nogat in 1406. Now designated a UNESCO world heritage site, the fortified monastery, following multiple conservation efforts, stands as the world's largest castle measured by surface area. The Gothic-style brick walls surrounding the castle do little to hide the magnificent visual appeal of the castle's rising interior.

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USS Nimitz

Deployed in 1975, the USS Nimitz—which would become the namesake for an entire class of aircraft carriers—ran 1,092 feet long, with a flight deck of 252 feet. The supercarrier could cruise at more than 30 knots (just over 34 miles per hour). With the ability to hold more than 5,000 servicemembers and 60 aircraft, the nuclear-powered floating fortress soon became the hallmark for the U.S. Navy, with a total of 10 Nimitz-class carriers that are still in service as the Navy's largest vessels.

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Fort Knox

The U.S. effort to build new military installations after WWI led to the start of Ft. Knox in 1918. Over years, the security and fortification has continued to increase, especially as the fort became home to the United State Bullion Depository, home of the largest portion of the country's official gold reserves. That security starts with an open field and includes layers of granite, concrete, and steel barriers, and that's before you even get to a safe that was built to withstand atomic bombs. Add in the presence of the U.S. Army, digital and visual surveillance, and the potential for every high-tech form of defense imaginable (there are fun rumors of flooding tunnels) and you get America's most secure safe. Of course, nobody really knows how much gold—or valuables of all sorts—is located within the bowels of Fort Knox.

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Fort Sumter

Following the War of 1812, the U.S. Army decided that the port city of Charleston, South Carolina, needed a stronger defense against the threat of naval attack, leading to the 1830 construction of Fort Sumter. Located on a small, rocky island in the center of Charleston Harbor, the 70,000-ton granite fort included a multi-tiered battery of artillery. Later, Ft. Sumter would earn iconic status as the site of the first shots of the American Civil War. Confederates gained control of the fort early on, and after rebuilding it for their own uses, were able to fend off the Union Army here throughout the war.

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The Alamo

Let's be clear: The Alamo was built as a Roman Catholic mission, not a fort. But the limestone structure became a fortification, and a legend in the mind of Texans, when it became a defensive structure during an attack by Santa Anna and his army in 1836. While the chapel stands as the largest structure on site, this four-acre complex includes limestone and adobe structures used by the Texans when the Mexican Army bombarded them, giving us the "Remember the Alamo" battle cry.

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Saxon Bastille

Perched on a rocky tabletop hill near Dresden, the Konigstein Fortress (or the Saxon Bastille) in Saxon Switzerland, Germany, overlooks the River Elbe. It's one of the largest fortresses in Europe, and entails four centuries of history built up over 50 buildings, including Germany's oldest preserved barracks. Along with the sandstone walls up to 137 feet tall and a rampart of nearly 6,000 feet, the Saxon Basille also has a 500-foot well in the center.

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Castillo de San Marcos

It is fitting that the oldest continually occupied European-established city in the United States—St. Augustine, Florida—also has one of the nation's oldest and most unique forts. After attacks on the Spanish-settled community endangered the residents, a star-shaped stone fort was built, the oldest masonry fort in the U.S. A moat that used a series of floodgates surrounded the walls, and an artificial slope added another touch to the 1600s-built fortification. Now located in downtown St. Augustine, the 2.5-acre fort remains a popular tourist destination.

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Area 51

Sure, there are fences to keep you out. But this infamous stretch of Nevada wasteland isn't a fort in the sense of walls or moats. It's about psychological military fortification, and how desperately lots of people what to know what really happened here. The outlying test site associated with California's Edwards Air Force Base has been tied to all sorts of obscure experimentation and research, mostly about space aliens, leading to a powerful mental barrier and mystique surrounding Area 51.

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Fort Independence

When Europeans spotted what would be named Boston Harbor, the strategic military value was immediately obvious. First constructed in 1643, Fort Independence was constructed in granite on Castle Island in a star shape full of cannons to protect the mainland. While multiple rebuilds reshaped the fort over the years, the allure of Fort Independence remains today. It is the oldest continually fortified site by the English in the United States.

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Fort Murud-Janjira

Built on a rock island in the Arabian Sea near the coastal village of Murud, Fort Murud-Janjira is reachable only via the sea. With 21 bastions, the Indian fort was originally built in the 15th century, but enlarged over time. The main gate remains hidden until those approaching the fort come within less than 50 feet of the island. Another gate stands on the opposite side of the island.

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Zeljava Airbase

One of the largest underground structures in Europe, the Zeljava Airbase is tucked underground along the border between Croatia and Bosnia-Herzegovina. While monitoring airspace in Europe and offering an early warning system, the facility also served as a potential respite for nuclear attack. The Yugoslav wars ravaged the site, though, and it was booby-trapped with land mines to prevent its potential future use.

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Gerald R. Ford-class carriers

Scheduled for delivery to the U.S. Navy in 2016, the Gerald R. Ford-class aircraft carrier will replace both the Enterprise and Nimitz-class carriers with its ability to operate with nearly 700 fewer crew. Technology upgrades include the first all-electric utilities on a carrier, eliminating steam service lines, a new reactor style, an updated aircraft launch system, fresh radar, and more. The Gerald R. Ford class will get planes into the air faster, run more efficiently, and strike more quickly.

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Maunsell Forts

These fortified towers poking up in the Thames and Mersey estuaries were built to protect England from German submarines. The forts also watched for submarines and housed antiaircraft guns used throughout World War II. The small towers, grouped in six forts, were decommissioned in the 1950s but many still remain, today rising above the water level with rusted power and impressive intrigue.

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